The present invention pertains to a method for making metal matrix composites reinforced with substantially continuous fibers within a metal matrix.
Metal matrix composite""s (MMC""s) have long been recognized as promising materials due to their combination of high strength and stiffness combined with low weight. MMC""s typically include a metal matrix reinforced with fibers. Examples of metal matrix composites include aluminum matrix composite wires (e.g., silicon carbide, carbon, boron, or polycrystalline alpha alumina fibers in an aluminum matrix), titanium matrix composite wires and tapes (e.g., silicon carbide fibers in a titanium matrix), and copper matrix composite tapes (e.g., silicon carbon fibers in a copper matrix).
The presence of imperfections in the wire such as intermetallic phases, dry (i.e., uncoated) fiber, porosity as a result, for example, of shrinkage or internal gas (e.g., hydrogen or water vapor) voids, etc. are known to decrease properties such as strength the of the wire. These imperfections can result from impurities in constituents (i.e., material of the metal matrix and the fiber), incompatibility of constituents, as well as incomplete infiltration of the matrix material into fibers.
The use of some metal matrix composite wires as a reinforcing member in bare overhead electrical power transmission cables is of particular interest. The need for new materials in such cables is driven by the need to increase the power transfer capacity of existing transmission infrastructure due to load growth and changes in power flow due to deregulation.
The availability of a wider variety of wires, including a variety of different wire diameters, is desirable in providing greater design variation in cable constructions. For example, a wider variety of wires of different diameter can provide cables within a wider range of diameters, as well as a wider range of stiffness or flexibility. A wider range of diameters also allows for a wider range of cable designs, such as larger cable diameter, as well as simplicity of manufacture of cables. Thus, there is a need for a process of making a substantially continuous metal matrix composite wire with relatively large diameter.
Further, there is a continuing need for methods for making metal matrix composite articles such as wires and tapes having desired or enhanced performance characteristics such as high strength.
The present invention relates to continuous methods for making substantially continuous fiber metal matrix composites. Embodiments of the present invention pertain a method for making metal matrix composites (e.g., composite wires) having a plurality of substantially continuous, longitudinally positioned fibers contained within a metal matrix. The infiltration in the methods according to the present invention is conducted substantially at atmospheric pressure (about 1 atmosphere), as opposed to pressure infiltration methods for making metal matrix composite materials. Metal aluminum matrix composites made according to the present invention preferably exhibit desirable properties with respect to elastic modulus, density, coefficient of thermal expansion, electrical conductivity, and strength.
In one aspect, the present invention provides a method for making a continuous, elongated metal matrix composite article (e.g., wires and tapes), the method comprising:
providing a contained volume of molten metallic matrix material; evacuating a plurality of at least one of substantially continuous, longitudinally positioned ceramic, boron, or carbon fibers in a vacuum;
immersing the evacuated plurality of substantially continuous fibers into the contained volume of molten metallic matrix material, wherein the evacuated plurality of substantially continuous fibers is introduced under a vacuum into the molten metallic material;
imparting ultrasonic energy to cause vibration of at least a portion of the contained volume of molten metal matrix material to permit at least a portion of the molten metal matrix material to infiltrate into the plurality of fibers such that an infiltrated plurality of fibers is provided; and
withdrawing the infiltrated plurality of fibers from the contained volume of molten metallic matrix material under conditions which permit the molten metallic matrix material to solidify to provide a continuous, elongated metal composite article comprising a plurality of at least one of substantially continuous, longitudinally positioned ceramic, boron, or carbon fibers in a metal matrix.
Preferably, the plurality of fibers are in the form of a tow(s).
In another aspect, the present invention provides a method for making a continuous, elongated metal composite article (e.g., wires and tapes), the method comprising:
providing a contained volume of molten metallic matrix material (e.g., aluminum);
immersing a plurality of at least one of substantially continuous, longitudinally positioned ceramic, boron, or carbon fibers into the contained volume of molten metallic matrix material;
imparting ultrasonic energy to cause vibration of at least a portion of the contained volume of molten metal matrix material to permit at least a portion of the molten metal matrix material to infiltrate into the plurality of fibers such that an infiltrated plurality of fibers is provided, wherein the molten metallic matrix material has a hydrogen content less than 0.2 cm3/100 grams (preferably, less than 0.15 cm3/100 grams, more preferably, less than 0.1 cm3/100 grams) of metal (e.g., aluminum); and
withdrawing the infiltrated plurality of fibers from the contained volume of molten metallic matrix material under conditions which permit the molten metallic matrix material to solidify to provide a continuous, elongated metal composite article comprising a plurality of at least one of substantially continuous, longitudinally positioned ceramic, boron, or carbon fibers in a metal matrix.
Preferably, the plurality of fibers are in the form of a tow(s).
In another aspect, articles made by a method according to the present invention preferably has a length of at least 10 meters (preferably, at least 25 meters, 50 meters, 100 meters, 200 meters, 300 meters, 400 meters, 500 meters, 600 meters, 700 meters, 800 meters, 900 meters, 1000 meters, or more). In another aspect, articles made according to a method of the present invention preferably have a minimum dimension of at least 2.5 mm (more preferably, at least 3 mm or 3.5 mm) over a length of at least 10 meters (preferably, at least 25 meters, 50 meters, 100 meters, 200 meters, 300 meters, 400 meters, 500 meters, 600 meters, 700 meters, 800 meters, 900 meters, 1000 meters, or more). Certain preferred metal matrix composite articles made by a method according to the present invention have a have a minimum dimension in the range from about 2.5 mm to about 4 mm over a length of at least 10 meters (preferably, at least 25 meters, 50 meters, 100 meters, 200 meters, 300 meters, 400 meters, 500 meters, 600 meters, 700 meters, 800 meters, 900 meters, 1000 meters, or more).
In another aspect, wire made by a method of the present invention preferably has a length of at least 10 meters (preferably, at least 25 meters, 50 meters, 100 meters, 200 meters, 300 meters, 400 meters, 500 meters, 600 meters, 700 meters, 800 meters, 900 meters, 1000 meters, or more). In another aspect, wire made by a method according the present invention preferably has a diameter of at least 2.5 mm (more preferably, at least 3 mm or 3.5 mm) over a length of at least 10 meters (preferably, at least 25 meters, 50 meters, 100 meters, 200 meters, 300 meters, 400 meters, 500 meters, 600 meters, 700 meters, 800 meters, 900 meters, 1000 meters, or more). Certain preferred metal matrix composite wires made by the method of the present invention have a diameter in the range from about 2.5 mm to about 4 mm over a length of at least 10 meters (preferably, at least 25 meters, 50 meters, 100 meters, 200 meters, 300 meters, 400 meters, 500 meters, 600 meters, 700 meters, 800 meters, 900 meters, 1000 meters, or more).
As used herein, the following terms are defined as:
xe2x80x9cSubstantially continuous fiberxe2x80x9d means a fiber having a length that is relatively infinite when compared to the average fiber diameter. Typically, this means that the fiber has an aspect ratio (i.e., ratio of the length of the fiber to the average diameter of the fiber) of at least about 1xc3x97105, preferably, at least about 1xc3x97106, and more preferably, at least about 1xc3x97107. Typically, such fibers have a length on the order of at least about 50 meters, and may even have lengths on the order of kilometers or more, and for articles less than 50 meters in length, the length of the fibers is typically the length of the composite article.
xe2x80x9cLongitudinally positionedxe2x80x9d means that the fibers are oriented in the same direction as the length of the wire.